Background: This study aims to review the methodologies used to identify the needs, the existing needs assessment instruments and the main topics of needs explored among caregivers of patients with mild cognitive impairment to dementia.; Methods: MEDLINE, PsycINFO, The Cochrane Library and Web of science were searched from January 1980 to January 2017. Research studies in English or French were eligible for inclusion if they fulfilled the following criteria: quantitative, qualitative and mixed method studies that used instrument, focus group or semi-structured interviews to assess the informal caregiver's needs in terms of information, coping skills, support and service.; Results: Seventy studies (n = 39 quantitative studies, n = 25 qualitative studies and n = 6 mixed method studies) met the inclusion criteria and were included. Thirty-six quantitative instruments were identified but only one has been validated for the needs assessment of dementia caregivers: the Carer's Needs Assessment for Dementia (CNA-D). The main areas of needs explored in these instruments were: information, psychosocial, social, psychoeducational and other needs.; Conclusions: No instrument has been developed and validated to assess the needs of informal caregivers of patients with cognitive impairment, whatever the stage and the etiology of the disease. As the perceived needs of caregivers may evolve with the progression of the disease and the dementia transition, their needs should be regularly assessed.